In addition to reducing respiratory syncytial virus (RSV)–related hospitalizations and emergency department (ED) visits, nirsevimab (Beyfortus) may also reduce these events when they’re linked to other lower respiratory tract infections (LRTIs) in infants and young toddlers, per a meta-analysis published last week in JAMA Pediatrics.
For the study, a team led by York University researchers in Toronto analyzed 11 real-world observational studies involving 263,755 children up to 2 years old who received nirsevimab and 27,522 control patients. The studies, which spanned the entire RSV season, were published from January to June 2025.
Nirsevimab, a long-acting monoclonal antibody that confers passive immunity for infants up to 6 months old, was approved in 2023 to prevent RSV-related LRTIs in infants in their first year of life, as well as high-risk infants in their second year of life.
“Although several observational studies have examined these outcomes following nirsevimab administration, no pooled analysis has yet evaluated the extended real-world effectiveness of nirsevimab for these broader end points,” the investigators wrote.
62% effective against all-cause respiratory illness hospitalizations
The 11 studies were from Spain, France, the United States, and Chile. Compared with controls, nirsevimab was tied to an effectiveness of 62% against all-cause LRTI hospitalizations (odds ratio [OR], 0.38), 48% against all-cause LRTI ED visits (OR, 0.52), and 76% against RSV ED visits (OR, 0.24).
These findings suggest that nirsevimab provides real-world protective benefits beyond those demonstrated or recognized for RSV-specific outcomes.
No significant difference was seen in all-cause hospitalizations (OR, 0.56) between the two groups. Sensitivity analyses confirmed that the main findings were robust under multiple scenarios.
“These findings suggest that nirsevimab provides real-world protective benefits beyond those demonstrated or recognized for RSV-specific outcomes, further supporting its implementation in infant immunization programs to reduce the respiratory-related disease burden and health care utilization,” the researchers wrote.
They noted that the prevention of all-cause LRTIs, distinct from those caused by RSV, has been seen in both randomized clinical trials and real-world evidence.
“The most plausible explanation is that RSV accounts for a substantial proportion of medically attended respiratory illness during annual outbreaks—up to 80% in temperate regions—such that protection against RSV leads to reductions in all-cause respiratory illness,” they wrote.
“Consequently, estimates of nirsevimab effectiveness against all-cause respiratory outcomes, particularly those derived from studies conducted during peak RSV circulation, are likely driven by its protection against RSV-related illness,” they wrote.
